TY - JOUR
T1 - The Regional Ocean Modeling System (ROMS) 4-dimensional variational data assimilation systems. Part II - Performance and application to the California Current System.
AU - Moore, Andrew M.
AU - Arango, Hernan G.
AU - Broquet, Gregoire
AU - Edwards, Chris
AU - Veneziani, Milena
AU - Powell, Brian
AU - Foley, Dave
AU - Doyle, James D.
AU - Costa, Dan
AU - Robinson, Patrick
N1 - Funding Information: We are grateful for the continued and unwavering support of the Office of Naval Research (N00014–01-1–0209, N00014–06-1–0406, N00014–08-1–0556, N00014–10-1–0322). Development of R4D-Var and 4D-PSAS was also supported by the National Science Foundation (OCE-0628690, OCE-0121176, OCE-0121506). Any opinions, findings, and conclusions or recommendations expressed here are those of the authors and do not necessarily reflect the views of the National Science Foundation. Part of this work was also supported by the National Ocean Partnership Program (NA05NOS4731242). J. Doyle acknowledges support through the Office of Naval Research’s Program Element 0601153N. We are also indebted to Anthony Weaver at CERFACS for countless discussions and much advice on various 4D-Var issues. COAMPS® is a registered trademark of the Naval Research Laboratory.
PY - 2011/10
Y1 - 2011/10
N2 - The Regional Ocean Modeling System (ROMS) 4-dimensional variational (4D-Var) data assimilation systems have been systematically applied to the mesoscale circulation environment of the California Current to demonstrate the performance and practical utility of the various components of ROMS 4D-Var. In particular, we present a comparison of three approaches to 4D-Var, namely: the primal formulation of the incremental strong constraint approach; the dual formulation " physical-space statistical analysis system" ; and the dual formulation indirect representer approach. In agreement with theoretical considerations all three approaches converge to the same ocean circulation estimate when using the same observations and prior information. However, the rate of convergence of the dual formulation was found to be inferior to that of the primal formulation. Other aspects of the 4D-Var performance that relate to the use of multiple outer-loops, preconditioning, and the weak constraint are also explored. A systematic evaluation of the impact of the various components of the 4D-Var control vector (i.e. the initial conditions, surface forcing and open boundary conditions) is also presented. It is shown that correcting for uncertainties in the model initial conditions exerts the largest influence on the ability of the model to fit the available observations. Various important diagnostics of 4D-Var are also examined, including estimates of the posterior error, the information content of the observation array, and innovation-based consistency checks on the prior error assumptions. Using these diagnostic tools, we find that more than 90% of the observations assimilated into the model provide redundant information. This is a symptom of the large percentage of satellite data that are used and to some extent the nature of the data processing employed. This is the second in a series of three papers describing the ROMS 4D-Var systems.
AB - The Regional Ocean Modeling System (ROMS) 4-dimensional variational (4D-Var) data assimilation systems have been systematically applied to the mesoscale circulation environment of the California Current to demonstrate the performance and practical utility of the various components of ROMS 4D-Var. In particular, we present a comparison of three approaches to 4D-Var, namely: the primal formulation of the incremental strong constraint approach; the dual formulation " physical-space statistical analysis system" ; and the dual formulation indirect representer approach. In agreement with theoretical considerations all three approaches converge to the same ocean circulation estimate when using the same observations and prior information. However, the rate of convergence of the dual formulation was found to be inferior to that of the primal formulation. Other aspects of the 4D-Var performance that relate to the use of multiple outer-loops, preconditioning, and the weak constraint are also explored. A systematic evaluation of the impact of the various components of the 4D-Var control vector (i.e. the initial conditions, surface forcing and open boundary conditions) is also presented. It is shown that correcting for uncertainties in the model initial conditions exerts the largest influence on the ability of the model to fit the available observations. Various important diagnostics of 4D-Var are also examined, including estimates of the posterior error, the information content of the observation array, and innovation-based consistency checks on the prior error assumptions. Using these diagnostic tools, we find that more than 90% of the observations assimilated into the model provide redundant information. This is a symptom of the large percentage of satellite data that are used and to some extent the nature of the data processing employed. This is the second in a series of three papers describing the ROMS 4D-Var systems.
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U2 - https://doi.org/10.1016/j.pocean.2011.05.003
DO - https://doi.org/10.1016/j.pocean.2011.05.003
M3 - Article
SN - 0079-6611
VL - 91
SP - 50
EP - 73
JO - Progress in Oceanography
JF - Progress in Oceanography
IS - 1
ER -